Is it normal for a dragon's body to disappear and for it to keep attacking the same place again?

I've killed a Dragon at both Winterhold and the College of Winterhold several times. In fact, if it is the same dragon as the one at Mount Anthor, I've killed it a couple of times more. It started out as a simple dragon and it is now a blood dragon. I think it might have been getting tougher to reflect my level. I think I've killed it around ten times already. It's skeleton disappears everytime I leave the place (I think I fast travelled every time) and come back (usually after some in game days, other quests and the like take up time. (:), it is no longer there. After spending some time in the area, it always appears and I end up killing it yet again, getting another dragon soul and other loot. I was wondering if this was a bug or if this was normal dragon behavior. I thought dragon bodies were not supposed to disappear?

Note: As evidenced by my other question, I have had bugged dragons before. The one in that question ended up appearing as a dead body at another quest location for no reason after all the trouble I explained earlier. This is just in case anyone is looking at both questions and there is a relation.

Thanks for taking the time to read this.